The invention relates to a method according to the preamble of claim 1. The usage of keyframes as representative parts of a video presentation, that is recorded for subsequent selective playback, has been proposed elsewhere. A continuous video stream means that video remains "on", which may include animation, a series of stills, or an interactive sequence of images. The character may be various, such as film, news, or for example a shopping list. State of the art is represented by the article `Content-Based Video Indexing and Retrieval` by S. W. Smoliar and H. J. Zhang, IEEE Multimedia, Summer 1994, pages 62-72.
Keyframes may be derived from video material upon its reception at the user's through a derivation algorithm, or keyframes may be labelled as such by a video provider, for example, in that each video shot will start with a keyframe. A third scheme is that the frames succeed each other with uniform time intervals as relating to standard video speed. The present invention recognizes that keyframes should be utilized so as to give users a dynamic overview over the presentation, combined with useful facilities for enabling them to easier access the material, for selecting or deselecting for subsequent display, or for editing.
A particular problem with present-day projects for digital and compressed coding of video images is that storage thereof on mass media generally does not allow immediate access thereto, in particular in that the linear storage density such as expressable in frames per storage size is non-uniform. It has been proposed to supplement a high-capacity main storage medium such as tape with a secondary storage medium with smaller capacity and enhanced accessibility. In that case, the execution of trick modes, such as fast forward and fast reverse, as well as editing of the video material for subsequent presentation in an abstracted, modified, or rearranged form give rise to appreciable difficulties, both as seen from the aspect of the user interface, as well as perceived from the aspect of storage technology.